This invention relates to a microwave heating apparatus and in particular an improvement in the arrangement of a magnetron in a heating oven chamber of a microwave heating apparatus.
A conventional microwave heating apparatus such as a microwave oven etc. is so arranged that only the output section, i.e., an antenna, of a magnetron is projected within a heating oven chamber in which a substance to be heated is placed. That is, the magnetron is mounted on the wall surface of the heating oven chamber, only the output section of the magnetron is projected within the heating oven chamber and a magnetron body including an anode cylinder, a magnet device etc. is positioned outside of the oven chamber. Where the magnetron is so arranged that a microwave is radiated through a waveguide toward a substance to be heated, only the output section of the magnetron is located in the waveguide and the remaining magnetron body is arranged outside the waveguide. The reason why the magnetron is so arranged is as follows. In order for the magnetron to effect a proper operation it is necessary that the magnetron body, particularly the anode cylinder, is cooled through direct exposure to an outer air. When the magnetron is in an oscillating state, the temperature of the magnetron body is raised up to about 400.degree. to 500.degree. C. If the magnetron body is left heated at that temperature, the magnetron ceases to be operated properly.
A heat generated at the anode cylinder is generally known as an anode loss and this heat energy accounts for 40 to 50% of a whole electric energy applied to the magnetron and the remaing 60 to 50% electric energy is substantially converted into a microwave output. Almost all of such an unconverted energy is dissipated outside of the heating oven chamber without being utilized.
Furthermore, since the magnetron body is placed outside of the heating oven chamber, the microwave heating apparatus itself is made large-sized, taking up an extra space.